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Cognition and Face Decoding
A Bands Frequency Analysis
Michela Balconi (michela.balconi@unicatt.it)
Department of Psychology, L.go Gemelli, 1
Milan, 20123 Italy
Claudio Lucchiari (bijol2@virgilio.it)
Department of Psychology, L.go Gemelli, 1
Milan, 20123 Italy
Introduction
EEG frequencies are traditionally subdivided in frequency
bands such as theta (4-8 Hz), alpha (8-12 Hz), beta (about
14-30 Hz) and gamma (around 40 Hz). During stimulation,
the simultaneously recorded responses of different EEG
frequency bands differ from each other (Pfurtscheller and
Neuper, 1992), and reflect different cognitive and mental
processes or states (Klimesch et al., 1998). Oscillations of
different EEG frequencies are associated with different
mental processes. Episodic memory processes seem to be
reflected as oscillations in the EEG theta frequencies (4-8
Hz). In contrast, 8-10 Hz alpha activity seems to be
modulated as a function of attentional demands whereas 10-
12 Hz alpha activity is modulated by stimulus-related
aspects, and/or semantic memory processes. The event
related decrease in EEG power is termed "event-related
desynchronization" (ERD) (Pfurtscheller, 1977) while
synchronization, or "event-related synchronization" (ERS)
denotes the increase in power (Pfurtscheller, 1992). The aim
of our study was to analyse the emotional decoding in face
processing through EEG indexes. In particular, we aimed to
study the differences between the EEG activity elicited by
emotional stimuli vs neutral stimuli. By analyzing event-
related changes in induced band power in narrow frequency
bands of the human electroencephalograph, the present
study explored a possible functional role of the alpha and
theta rhythms during the processing of face with an
emotional content.
Methods
Event-related synchronization (ERS) in response to neutral,
positive and negative emotional faces were measured in
theta and alpha frequency bands in 20 healthy right-handed
subjects. A 14-channel EEG was recorded while subjects
viewed a sequence of 70 face pictures displayed by a
computer station. An EOG channel monitored eye
movements. Artefacts were rejected by an automatic
rejection procedure and a following morphological analysis.
The effects of the emotional decoding process was
evaluated between 200 and 300 ms post-stimulus in relation
to the N230 ERP component (Helgren and Marinkovic,
1995).
Results and Discussion
Theta ERS revealed a significant valence by hemisphere
interaction for anterior sites indicating a relatively greater
right hemisphere ERS for negative and a left hemisphere
ERS for positive stimuli in comparison to neutral ones. In
the alpha band, negative stimuli induced a left hemisphere
ERS increase not observed for neutral and positive stimuli.
The results obtained along with the earlier observations on
EEG correlates (Balconi & Pozzoli, 2003; Balconi &
Lucchiari 2005) of affective processing shows that
emotional decoding from face elicits specific EEG activity,
particularly in theta and alpha frequency bands.
References
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Balconi, M., & Pozzoli, U. (2003). Face-selective
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Halgren, E. & Marinkovic, K. (1995). Neurophysiological
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Klimesch, W., Russegger, H., Doppelmayr M., Pachinger T.
(1998). Induced and evoked band power changes in an
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Klimesch, W., Schimke, H., & Schweiger, I. (1994).
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Article
[discuss] human emotional neurophysiology / postulate on the existence of an emotional system consisting of an orienting complex, event integration, and response selection / a cortico-limbic-brainstem network is described as the neural instantiation of these processes (PsycINFO Database Record (c) 2012 APA, all rights reserved)
Changes in the background EEG activity occurring at the same time as visual and auditory evoked potentials, as well as during the interstimulus interval in a CNV paradigm were analysed in human subjects, using serial power measurements of overlapping EEG segments. The analysis was focused on the power of the rhythmic activity within the alpha band (RAAB power). A decrease in RAAB power occurring during these event-related phenomena was indicative of desynchronization. Phasic, i.e. short lasting, localised desynchronization was present during sensory stimulation, and also preceding the imperative signal and motor response (motor preactivation) in the CNV paradigm.
Oscillations in the alpha and beta bands can display either an event-related blocking response or an event-related amplitude enhancement. The former is named event-related desynchronization (ERD) and the latter event-related synchronization (ERS). Examples of ERS are localized alpha enhancements in the awake state as well as sigma spindles in sleep and alpha or beta bursts in the comatose state. It was found that alpha band activity can be enhanced over the visual region during a motor task, or during a visual task over the sensorimotor region. This means ERD and ERS can be observed at nearly the same time; both form a spatiotemporal pattern, in which the localization of ERD characterizes cortical areas involved in task-relevant processing, and ERS marks cortical areas at rest or in an idling state.
Article
Previous studies have revealed that decoding of facial-expressions starts very early in the brain ( approximately 180 ms post-stimulus) and might be processed separately from the basic stage of face perception. In order to explore brain potentials (ERPs) related to decoding of facial-expressions and the effect of emotional valence of the stimulus, we analyzed 18 normal subjects. Faces with five basic emotional expressions (fear, anger, surprise, happiness, sadness) and neutral stimulus were presented in random order. The results demonstrated that an emotional face elicited a negative peak at approximately 230 ms (N230), distributed mainly over the posterior site for each emotion. The electrophysiological activity observed may represent specific cognitive processing underlying the decoding of emotional facial-expressions. Nevertheless, differences in peak amplitude were observed for high-arousal negative expressions compared with positive (happiness) and low-arousal expressions (sadness). N230 amplitude increased in response to anger, fear and surprise, suggesting that subjects' ERP variations are affected by experienced emotional intensity, related to arousal and unpleasant value of the stimulus.
Neurophysiological networks integrating human emotions The Cognitive Neurosciences Induced and evoked band power changes in an oddball task
  • E Halgren
  • K W Marinkovic
  • H Russegger
  • M Doppelmayr
  • T Pachinger
Halgren, E. & Marinkovic, K. (1995). Neurophysiological networks integrating human emotions. In M.S. Gazzaniga, (Ed.). The Cognitive Neurosciences. Cambridge: MIT Press. Klimesch, W., Russegger, H., Doppelmayr M., Pachinger T. (1998). Induced and evoked band power changes in an oddball task. Electroencephalography and Clinical Neurophysiology, 108, 123-130.
Induced and evoked band power changes in an oddball task
  • E Halgren
  • K Marinkovic
  • W Klimesch
  • H Russegger
  • M Doppelmayr
  • T Pachinger
Halgren, E. & Marinkovic, K. (1995). Neurophysiological networks integrating human emotions. In M.S. Gazzaniga, (Ed.). The Cognitive Neurosciences. Cambridge: MIT Press. Klimesch, W., Russegger, H., Doppelmayr M., Pachinger T. (1998). Induced and evoked band power changes in an oddball task. Electroencephalography and Clinical Neurophysiology, 108, 123-130.